This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-353174, filed Dec. 13, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a cooling unit for promoting heat radiation of circuit components that generate heat, such as a semiconductor package, and an electronic apparatus such as a personal computer comprising the cooling unit.
An electronic apparatus such as a desktop personal computer and a workstation comprises a semiconductor package for multi-purpose multimedia information such as characters, speech and images. In the semiconductor package of this kind, the power consumption is increased in accordance with the acceleration of the processing speed and the versatility, and in proportion to this the amount of heat in the operation is also inclined to rapidly increase.
For this reason, heat radiation of the semiconductor package needs to be enhanced to maintain the stable operation thereof. Therefore, various heat radiating/cooling means such as a heat sink or a heat pipe are indispensable.
A conventional heat sink has a heat receiving portion thermally connected to the semiconductor package. If there is a poor contact between the heat receiving portion and the semiconductor package, a gap occurs therebetween and thereby prevents transfer of the heat from the semiconductor package to the heat receiving portion. Thus, in the prior art, heat conductive grease or a rubber heat transfer sheet is provided between the heat receiving portion and the semiconductor package and the heat sink is pressed against the semiconductor package through a spring to enhance the close contact between the heat receiving portion and the semiconductor package.
Incidentally, if the heat receiving portion of the heat sink is forcibly pressed against the semiconductor package, load is applied to the semiconductor package through the heat receiving portion and may be the stress to the semiconductor package. In this case, there is no problem if the semiconductor package has strength enough to overcome the stress. Recently, however, the semiconductor package has been structurally simplified due to various requests such as reduction of the manufacturing costs, saving of the weight, miniaturization and the like. For this reason, some kinds of the semiconductor packages do not have the structural strength enough to bear the stress.
Specifically, in the ceramic package, which is a typical airtight sealing package, an IC chip generating heat is covered with a ceramic board or a ceramic lid having high rigidity. The load of the heat sink can be therefore received by the ceramic board or the ceramic lid.
On the other hand, in the BGA (Ball Grid Array) package and PGA (Pin Grid Array) package in which the IC chip is subjected to flip chip bonding on a synthetic resin circuit board, or the TCP (Tape Carrier Package) in which the IC chip is bonded to polyimide tape, the IC chip is exposed to the outside and the circuit board or tape supporting the IC chip is formed of synthetic resin. For this reason, it cannot be said that the package of this kind has the strength enough to bear the load from the heat sink.
Therefore, for example, if the heat receiving portion of the heat sink is pressed against the IC chip of the BGA package, the stress concentrates on the IC chip and the IC chip may be broken. In addition, as the IC chip receives the load caused by pressing the IC chip against the circuit board, the load acts as a bending force to the circuit board and the circuit board may be curved or bent backward. As a result, the stress is continuously applied to the connection portions of the IC chip and the circuit board, which may cause the faulty bonding.
Therefore, the heat sink cannot be pressed against the IC chip with a large force in the semiconductor package such as the BGA, PGA and the like. For this reason, it is difficult to sufficiently maintain the close contact between the heat sink and the semiconductor package, and efficient transfer of heat from the semiconductor package to the heat sink is prevented.
The object of the present invention is to provide a cooling unit and circuit module capable of efficiently radiating the heat of the circuit component to the heat sink while reducing the stress applied to the circuit components, and also provide an electronic apparatus comprising the cooling unit.
In one embodiment of the invention, there is provided an apparatus comprising a wiring board having a surface; a circuit component containing a base of synthetic resin, said base having a first mounting surface, a second mounting surface positioned on an opposite side to the first mounting surface, a plurality of terminals arranged on said second mounting surface, and a heat generating unit positioned on a central part of the first mounting of said base, said plurality of terminals arranged in an area around said heat generating unit; a socket provided on the surface of said wiring board and electrically connected to said plurality of terminals, said socket having a hollow portion at a position corresponding to the central part of said base, said second mounting surface of said base facing the hollow portion of said socket; a heat sink on said circuit component, said heat sink having a heat receiving portion for receiving heat of said heat generating unit; a flexible heat-transfer member provided between said heat generating unit and said heat receiving portion, for thermally connecting said heat generating unit and said heat receiving portion; and a spacer provided between said base of said circuit component and said heat sink, for supporting said heat sink.
In another embodiment of the invention, there is provided an electronic apparatus comprising a housing; a wiring board contained inside said housing, said wiring board having a surface; a circuit component containing a base, said base having a first mounting surface, a second mounting surface positioned on an opposite side to the first mounting surface, a plurality of terminals arranged on said second mounting surface, said plurality of terminals, said socket having a hollow portion at a position corresponding to the central part of said base, said second mounting surface of said base facing the hollow portion of said socket; a heat sink on said circuit component, said heat sink having a heat receiving portion for receiving heat of said heat generating unit; a flexible heat-transfer member provided between said heat generating unit and said heat receiving portion, for thermally connecting said heat generating unit and said heat receiving portion to one another; a pushing member for pushing said heat sink toward said heat generating unit to sandwich said heat-transfer member between said heat generating unit and said heat receiving portion; and a spacer provided between said base of said circuit component and said heat sink, for supporting said heat sink.
In this structure, when the heat sink is thermally connected to the heat generating unit, the heat sink is pushed on the heat generating unit by the pushing means. At this time, as the spacer is provided between the heat sink and the base of the circuit component, most of the load of heat sink applied to the heat generating unit is received by the spacer. Thus, excessive stress is not concentrated on the heat generating unit and thereby bending or warping of the base supporting the heat generating unit can be prevented. For this reason, it is possible to prevent floating of the heat generating unit or damage of the mounting part of the heat generating unit.
In addition, the close contact between the heat generating unit and the heat receiving portion can be maintained by appropriately pushing down the flexible heat-transfer member between the heat receiving portion and the heat generating unit. Therefore, the thermal connection between the heat generating unit and the heat receiving portion can be stably maintained and the heat of the heat generating unit can be efficiently transferred to the heat sink.
To achieve the above-described object, there is also provided a cooling unit according to the present invention, for cooling a circuit component including base of synthetic resin having a mounting surface and a heat generating unit mounted on the mounting surface of the base. The cooling unit comprises a heat sink, which is overlapped on the circuit component and which has a heat receiving portion for receiving heat of the heat generating unit, a spacer, which is provided between the base and the heat sink and which constitutes a grease-filled chamber surrounding the heat generating unit in cooperation with the base and the heat sink, fixing means for fixing the heat sink on the base to allow the spacer to be sandwiched between the heat sink on the base, and heat-transfer grease packed in the grease-filled chamber to thermally connect the heat generating unit and the heat sink to one another.
In this structure, as the heat generating unit is embedded in the grease, the contact area of the heat generating unit and the grease and the contact area of the heat sink and the grease can be adequately maintained. Therefore, the heat of the heat generating unit can be efficiently transferred to the heat sink through the grease.
Moreover, if the heat sink is fixed on the base, the spacer is sandwiched between the heat sink and the base. Thus, the heat generating unit is not directly pushed down by the heat sink or no stress is not applied to the heat generating unit. In addition, the load of the heat sink applied to the base when the heat sink is fixed is dispersed in a wide range around the heat generating unit via the spacer, and the excessive stress cannot be concentrated on a specific part of the base. Therefore, it is possible to prevent the bending or warping of the base supporting the heat generating unit, and also possible to prevent the floating of the heat generating unit or damage of the mounting part of the heat generating unit.
To achieve the above-described object, there is also provided a circuit module according to the present invention, comprising a wiring board, a semiconductor package containing a circuit board of synthetic resin, which has a mounting surface and a plurality of current-carrying terminals on a opposite side to the mounting surface, and an IC chip, which is mounted on the mounting surface of the circuit board and generates heat, the current-carrying terminals being electrically connected to the wiring board, a heat sink, which is overlapped on the semiconductor package and which has a heat receiving portion for receiving heat of the IC chip, a flexible heat-transfer member provided between the IC chip and the heat receiving portion, for thermally connecting the IC chip and the heat receiving portion to one another, pushing means for pushing the heat sink toward the IC chip to sandwich the heat-transfer member between the IC chip and the heat receiving portion, and a spacer provided between the circuit board of the semiconductor package and the heat sink, for supporting the heat sink, at a position remote from the IC chip.
In this structure, when the heat sink is thermally connected to the IC chip of the semiconductor package, the heat sink is pushed on the IC chip by the pushing means. At this time, as the spacer is provided between the heat sink and the circuit board of the semiconductor package, most of the load of heat sink applied to the IC chip is received by the spacer. Thus, excessive stress is not concentrated on the IC chip and thereby the bending or warping of the circuit board supporting the IC chip can be prevented. For this reason, it is possible to prevent the floating of the IC chip or the damage of the mounting part of the IC chip.
Further, the load applied to the circuit board through the spacer is transferred to the wiring board via a plurality of current-carrying terminals. Therefore, the load on each of the current-carrying terminals can be reduced, deformation or breakage of the current-carrying terminals can be prevented, and the damage of the connecting part between the current-carrying terminals and the wiring board can also be prevented.
In addition, the close contact between the IC chip and the heat receiving portion can be maintained by appropriately pushing down the flexible heat-transfer member between the IC chip and the heat receiving portion. Therefore, the thermal connection between the IC chip and the heat receiving portion can be stably maintained and the heat of the IC chip can be efficiently transferred to the heat sink.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.